JP-A 6-331019 discloses a shift mode selector for an automatic transmission. According to this known mode selector, an operator can select one of a plurality of shift modes. The shift modes that may be selected by the operator include an automatic shift (D) mode and a manual shift (M) mode as a special shift mode fit for a particular purpose. Upon operator selection of a drive range in the automatic shift (D) mode, a microprocessor retrieves data from a drive range shift point map against engine load signal and vehicle speed signal and processes the retrieved data to produce a gear ratio control signal. A gear ratio control actuator is operable in response to the gear ratio control signal to establish various gear ratios in the automatic transmission. Upon operator selection of the manual shift (M) mode, the microprocessor receives an operator upshift or downshift demand, retrieves data from a manual range shift point map and processes the retrieved data and the operator upshift or downshift demand to produce the gear ratio control signal. Basically, the gear ratio control actuator establishes a gear ratio desired by the operator if the operator upshift or downshift demand is valid in view of current engine load signal and vehicle speed signal.
The control system employed by the known shift mode selector is fairly developed. However, a need remains for further development of such control systems, particularly in view of current movement to increase user satisfaction at less cost increase.